Re: 1968 18hp evinrude fastwin
Having jumped out of gear so many times, not only will the clutch dog be damaged but also the 'ears' on the forward gear.
You should replace both, as a damaged forward gear will ruin a new dog clutch in short order.
With some motors, you're able to swap fwd and reverse gears but I expect your fwd gear wouldn't do so well even when used as a reverse gear.
Note that on many of these smaller OMC's, either the gears are directly interchangeable, or in the case of fwd gears that have a bronze thrust bushing pressed onto the gear (see bushing, #34 in the O.P.'s parts diagram), the bushing can be pressed out and pressed-into the reverse gear and then used in the fwd position. The reverse gear bushing is just a slip-fit and would also fit the swapped-in gear in the same fashion.
This does open up possibilities of finding a relatively unworn good reverse gear out of a donor motor then utilizing it as a fwd gear.
Typically, reverse gears won't have as much wear on them, since you'd typically be spending much more time shifting in and out of fwd gear.
At any rate, don't run it any more, it'll just make more metal chunks circulate in the gears and that can't be good for the remaining parts.
You can do this work without even pulling the lower unit from the motor, but it's a lot easier to remove the lower unit and (after draining gear oil) flipping it upside-down, carefully mounted in a vice, etc.
While you're in there you might also consider replacing the shift-shaft O-ring (lots of posts here on doing that particular job), and renewing driveshaft oil seals. Check the propshaft seal(s) carefully and replace as needed.
Replace the prop shaft carrier O-ring and pick up a length of gearcase "spaghetti" O-ring seal for the groove in the gearcase half.
Seal the gearcase housing with Permatex #3 non-hardening Aviation-type gasket dressing. Use Permatex on the threads of the gearcase screws, also. This'll ensure it comes apart easily for any required maint in the future.
Note, a hand-impact scredriver comes in real handy when busting the screws loose on the gearcase halves. Very easy to strip out the heads otherwise.
Last Thought, make sure the shift linkage under the powerhead isn't sloppy (a common problem) as this'll promote further wear on the replaced parts. And adjust the shifter afterwards to make sure there is a bit of preload when in fwd gear, this'll help it stay in gear.
HTH & G'luck with the repairs...........ed
